A rocket fired by militants in Gaza struck the western Negev on Wednesday morning, adding impetus to flare-up in violence that threatened to rupture a shaky cease-fire in the coastal strip.

No one was wounded in the rocket attack, which came shortly after Israel Air Force warplanes pounded smuggling tunnels under Gaza's border with Egypt. The air strikes followed a bomb blast Tuesday along the Israel-Gaza border, in which an Israel Defense Forces soldier was killed and three others were wounded.

Rafah residents began to flee their homes in panic as the Israeli aircraft struck three times, Hamas officials said. There was no initial word of any casualties.

An Israel Defense Forces spokesman said the air strike came in response to a remote-control bomb attack at the Gaza Strip security fence Tuesday, which killed an Israel Defense Forces tracker and wounded three other soldiers, one seriously.

The border blast was the Palestinians' first deadly attack since the cease-fire ended Operation Cast Lead, and came the day before the arrival of George Mitchell, the U.S. envoy to the Middle East.

Earlier on Tuesday, IAF aircraft fired a missile at a militant on a motorbike in the Khan Yunis area of Gaza. The Shin Bet security service, which helped coordinate the missile strike, said the militant, Hussein Abu-Shamaya, was involved in the bomb attack. The bomb was planted by a Hamas breakaway group identified with the Al-Qaida-affiliated Global Jihad, the Shin Bet said.

In addition, a Palestinian man, apparently a farmer, was killed in exchanges of fire between IDF troops and Palestinians in Gaza after the bomb was detonated, according to Palestinian reports. The incident took place while IDF tanks and soldiers, assisted by helicopters, were patrolling Gaza after the attack.

Prime Minister Ehud Olmert warned of a "further response" to the attack.

"What the IDF did today was not a response but a preliminary action," he said at a meeting of ministry directors general. "A further response to this serious incident will be forthcoming."

The security cabinet is to meet Wednesday to discuss security projects, but the situation in Gaza might also be discussed.

Olmert, noting that he had termed the cease-fire "fragile," also said: "We don't even call it a cease-fire but a holding of fire in the face of Hamas infractions, so that we can retain the IDF's freedom of action."

Defense Minister Ehud Barak decided to strike Hamas targets in response to the death of the tracker.

"We do not intend to gloss over incidents like these," Barak said. "We will not let Hamas and its outgrowths continue their hostile acts of terror. Anyone who hits us will have to absorb a serious blow in the future, too."

Sources in the Prime Minister's Bureau said Tuesday Israel was not negotiating with Hamas over a cease-fire or second lull. "The Egyptians are speaking to Hamas to attain things that are important for them, but we are not obligated to anything. We have not signed understandings or an agreement with Hamas," a source in Olmert's bureau said.

Israel and Egypt are apparently formulating an understanding on the passage of merchandise from Israel to the Gaza Strip, and at the same time some increased freedom of movement in the opening of the Rafah crossing from the Strip to Egypt.

The Kerem Shalom and Karni crossings on the Gaza border were closed after the attack. Approximately 185 trucks carrying aid and equipment were to have crossed into Gaza yesterday.

The bomb near the Gaza border detonated around 8 A.M., as an IDF patrol was passing near the Kissufim crossing, north of Kibbutz Kissufim. The tracker was killed and an officer was seriously hurt. One of his legs was amputated and the other one is severely damaged. Two other soldiers were classified as lightly hurt and will be released in a few days. Soroka Medical Center said they had extensive shrapnel wounds.

The name of the tracker, a Bedouin, was not released, at the request of his family.

A preliminary investigation revealed that the soldiers were patrolling an area that had not been patrolled for several weeks due to the fighting in the Strip. The regional brigade commander was apparently not apprised of the patrol, which was approved by the battalion commander. IDF sources said the Palestinians who planted the bomb did so Monday night, under cover of heavy fog.

The closure of the Gaza crossings is only the first stage of Israel's response to the attack, Amos Gilad, who heads the Defense Ministry's political bureau, said yesterday. "The equation in the Strip has changed," he said during a lecture at the Institute for National Security Studies in Tel Aviv.